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Decay of Leonardo da Vinci drawing reflected in light

RAVAGES OF TIME Damaged components of paper absorb blue and violet light, resulting in yellowing of ancient artwork, as seen in this early 16th century portrait by Leonardo da Vinci. Researchers have developed a noninvasive technique to quantify such damage.

M.C. Misiti/Central Institute for the Restoration of Archival and Library Heritage, Rome

An aged and wrinkled face drawn by Leonardo da Vinci, widely considered a self-portrait, is in danger of fading away. Using a new, harmless method to assess chemical damage of the red chalk drawing, researchers found significant decay in the cellulose fibers of the paper. Such damage leads to the characteristic yellowing of timeworn paper.

The method, developed by physicist Adriano Mosca Conte of the University of Tor Vergata in Rome and colleagues, uses the spectrum of light that bounces off paper.

Kept in poor conditions, such as high humidity, paper’s cellulose fibers break down into various chemicals. Some of these molecules, called chromophores, absorb violet and blue light but scatter red and yellow light, giving the paper the hue of age.

By measuring the reflected light in a particular range of wavelengths, Mosca Conte’s team estimated how many of the light-absorbing molecules had built up over time. They found that the early 16th century drawing has as many chromophores as other similarly aged papers with environmental damage. The results appear in the June 2 Applied Physics Letters.

The authors suggest that the new diagnostic method can help monitor the decay of artwork.